U.S. patent application number 12/515089 was filed with the patent office on 2009-12-10 for magnesium-based medical device and manufacturing method thereof.
Invention is credited to Sachiko Hiromoto, Norio Maruyama, Toshiji Mukai, Hidetoshi Somekawa, Akiko Yamamoto.
Application Number | 20090306725 12/515089 |
Document ID | / |
Family ID | 39401772 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090306725 |
Kind Code |
A1 |
Hiromoto; Sachiko ; et
al. |
December 10, 2009 |
MAGNESIUM-BASED MEDICAL DEVICE AND MANUFACTURING METHOD THEREOF
Abstract
A magnesium-based medical device which can adjust a degree of
corrosion within a wide range of period such that the device can
maintain a sufficient strength only during a desired period and
disappears within a desired period thereafter and a manufacturing
method thereof are provided. A magnesium-based medical device of
the present invention is a magnesium-based medical device in which
a base material is made of magnesium or a magnesium alloy, wherein
a corrosion-resistant film is formed on a surface of the base
material, and variation in surface hardness of the formed
corrosion-resistant film in the in-plane direction is less than 21
in terms of a dispersion value of Vickers hardness.
Inventors: |
Hiromoto; Sachiko; (Ibaraki,
JP) ; Yamamoto; Akiko; (Ibaraki, JP) ;
Maruyama; Norio; (Ibaraki, JP) ; Mukai; Toshiji;
(Ibaraki, JP) ; Somekawa; Hidetoshi; (Ibaraki,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39401772 |
Appl. No.: |
12/515089 |
Filed: |
November 16, 2007 |
PCT Filed: |
November 16, 2007 |
PCT NO: |
PCT/JP2007/072316 |
371 Date: |
July 2, 2009 |
Current U.S.
Class: |
606/298 ;
427/2.24; 606/77; 623/1.46 |
Current CPC
Class: |
A61L 27/00 20130101;
C23C 22/22 20130101; A61L 27/58 20130101; A61L 27/32 20130101; A61L
27/047 20130101 |
Class at
Publication: |
606/298 ;
427/2.24; 606/77; 623/1.46 |
International
Class: |
A61L 27/58 20060101
A61L027/58; C23C 22/22 20060101 C23C022/22; A61B 17/80 20060101
A61B017/80; A61F 2/82 20060101 A61F002/82 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2006 |
JP |
2006-311596 |
Claims
1-9. (canceled)
10. A magnesium-based medical device which has a base material made
of magnesium or a magnesium alloy and is dissolved and disappears
in a living body, wherein a corrosion-resistant film is formed on a
surface of the base material, and variation in a numerical value of
hardness of the formed film expressed in terms of Vickers hardness
is controlled corresponding to desired corrosion resistance.
11. A magnesium-based medical device according to claim 10, wherein
the corrosion-resistant film contains calcium phosphate.
12. A manufacturing method of the magnesium-based medical device
according to claim 10, being characterized in that, in a state that
the base material is immersed in a solution in which components for
forming the corrosion-resistant film are dissolved, a flow of the
solution whose flow speed is controlled is generated relative to
the surface of the base material thus depositing a
corrosion-resistant film on the surface of the base material.
13. The manufacturing method of the magnesium-based medical device
according to claim 12, wherein a degree of variation in a numerical
value of hardness of the formed corrosion-resistant film which is
expressed in terms of Vickers hardness in the in-plane direction is
adjusted by controlling the flow speed of the solution relative to
the surface of the base material.
14. The manufacturing method of the magnesium-based medical device
according to claim 12, wherein the base material is immersed in a
solution which contains phosphorous ions and calcium ions thus
forming the corrosion-resistant film containing calcium phosphate
on the surface of the base material.
15. A manufacturing method of the magnesium-based medical device
according to claim 11, being characterized in that, in a state that
the base material is immersed in a solution in which components for
forming the corrosion-resistant film are dissolved, a flow of the
solution whose flow speed is controlled is generated relative to
the surface of the base material thus depositing a
corrosion-resistant film on the surface of the base material.
16. The manufacturing method of the magnesium-based medical device
according to claim 13, wherein the base material is immersed in a
solution which contains phosphorous ions and calcium ions thus
forming the corrosion-resistant film containing calcium phosphate
on the surface of the base material.
17. The manufacturing method of the magnesium-based medical device
according to claim 15, wherein the base material is immersed in a
solution which contains phosphorous ions and calcium ions thus
forming the corrosion-resistant film containing calcium phosphate
on the surface of the base material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a magnesium-based medical
device and a manufacturing method thereof.
BACKGROUND ART
[0002] Conventionally, a metallic medical device which is used in
general remains in a body unless the medical device is removed by
an operation or the like after being embedded in the body.
Depending on applications, it is desirable that such a metallic
medical device maintains a mechanical strength during a period that
peripheral tissues are recovered, and is degraded and disappears
without requiring an operation after the recovery of the peripheral
tissues.
[0003] A magnesium material shows high corrosion rate in an
environment where chloride ions are present and hence, the use of
the magnesium material as a general-purpose-use material such as
parts of transportation equipment or household appliances is
limited. On the other hand, the magnesium material shows low
harmful property to a living body, and is corroded, is degraded and
disappears at an extremely high speed in an approximately neutral
aqueous solution containing chloride ions such as a body fluid.
Accordingly, the magnesium material is expected to be used as a
medical biodegradation metallic material which is gradually
degraded and absorbed after being embedded in a living body, so
that the development of the magnesium material has been under way
(see patent documents 1 and 2).
[0004] Depending on a kind of a device or a condition of an
affected part, a strength holding period which the device is
required to satisfy varies in an extremely wide range. For example,
with respect to a blood vessel treatment device such as a stent, it
is desirable that the device maintains a strength for a period of
five months to six months necessary for repairing a narrowed part
of a blood vessel, and the degradation of the whole device is
almost finished within one week to twelve weeks after the vessel is
repaired. This is because that when the stent remains in the blood
vessel even after the blood vessel wall is repaired, due to the
mechanical stimulation and chemical irritation which the stent
continuously contacts to the blood vessel wall, vascular
endothelial cells are excessively grown thus causing restenosis of
the blood vessel whereby the disappearance of the stent after
repairing of the blood vessel is extremely important.
[0005] On the other hand, with respect to a fracture fixation
device, it is desirable that the device supports a load during
three months to one year until fracture is cured and, thereafter,
the degradation of the whole device is almost finished within eight
month to five years.
[0006] In this manner, along with the degradation and disappearance
of the device after the fracture is cured, a load is gradually
applied to a cured bone and hence, it is possible to suppress the
load interception which is a phenomenon that the device supports
the load in place of the bone. This leads to the suppression of
re-fracture which occurs due to bone absorption (thinning of bone)
attributed to the load interception. Further, it is unnecessary to
perform an operation for taking out the device after the fracture
is cured and hence, a burden imposed on a patient can be reduced.
In this manner, the strength holding period which the device is
required to satisfy varies in a wide range, and may be a long
period of several months or more in some cases.
[0007] Accordingly, it is considered desirable if it could be
possible to control the progress of degradation during a period in
which the strength holding is required and a following period in
which degradation progresses. However, in case of the biodegradable
magnesium material proposed in patent document 1, for example, the
degradation period is controlled corresponding to a size of device.
Accordingly, in a living body where the degradation of the device
starts immediately after embedding of the magnesium material and,
at the same time, a space in which the device is to be embedded is
limited, there may be a case that the device having a necessary
size is not applicable whereby, it is substantially impossible to
properly use the magnesium material as a device which is required
to hold a strength for a particularly long period.
[0008] Further, with respect to a biodegradable magnesium material
which inventors of the present invention proposed in patent
document 2, the magnesium material is configured to control a
strength-ductility balance of the material and a degradation speed
of the material in a living body to desired values based on the
composition of the material or a control of the internal structure
of the material. For example, the degradation speed can be
controlled by controlling a kind and the concentration of an adding
element.
[0009] However, the control of the degradation speed due to the
formation of an alloy using an adding element is limited and hence,
the adjustment of the degradation period in a wide range is
difficult. That is, the concentration of the adding element in the
alloy is dependent on and defined by a desired strength-ductility
balance and hence, the limitation of the adjustment range of
corrosion resistance is inevitable.
Patent document 1: JP-A-2004-160236 Patent document 2:
International Publication WO2007/58276 brochure
DISCLOSURE OF THE INVENTION
Task to be Solved by the Invention
[0010] The present invention has been made in view of the
above-mentioned circumstances, and it is an object of the present
invention to provide a magnesium-based medical device and
manufacturing method thereof which can overcome the drawbacks of
the related art, and can adjust a degree of corrosion within a wide
range of period such that the device can maintain a sufficient
strength only during a desired period and disappears within a
desired period thereafter.
Means for Overcoming the Task
[0011] The present invention includes the following technical
features which can overcome the above-mentioned drawbacks.
[0012] First technical feature: A magnesium-based medical device in
which a base material is made of magnesium or a magnesium alloy,
wherein a corrosion-resistant film is formed on a surface of the
base material, and variation in surface hardness of the formed
corrosion-resistant film in the in-plane direction is less than 21
in terms of a dispersion value of Vickers hardness.
[0013] Second technical feature: The magnesium-based medical device
of the first technical feature, wherein the variation in surface
hardness of the formed corrosion-resistant film in the in-plane
direction is less than 12 in terms of the dispersion value of
Vickers hardness.
[0014] Third technical feature: The magnesium-based medical device
of the first technical feature, wherein the variation in surface
hardness of the formed corrosion-resistant film in the in-plane
direction is less than 10 in terms of the dispersion value of
Vickers hardness.
[0015] Fourth technical feature: The magnesium-based medical device
of the first technical feature, wherein the variation in surface
hardness of the formed corrosion-resistant film in the in-plane
direction is less than 8 in terms of the dispersion value of
Vickers hardness.
[0016] Fifth technical feature: The magnesium-based medical device
of the first technical feature, wherein the variation in surface
hardness of the formed corrosion-resistant film in the in-plane
direction is less than 7 in terms of the dispersion value of
Vickers hardness.
[0017] Sixth technical feature: The magnesium-based medical device
of any one of the first to fifth technical features, wherein the
corrosion-resistant film contains calcium phosphate.
[0018] Seventh technical feature: A manufacturing method of the
magnesium-based medical device according to any one of the first to
sixth technical features, being characterized in that, in a state
that the base material is immersed in a solution in which
components for forming the corrosion-resistant film are dissolved,
a flow of the solution whose flow speed is controlled relative to
the surface of the base material thus depositing the
corrosion-resistant film on the surface of the base material.
[0019] Eighth technical feature: The manufacturing method of the
magnesium-based medical device according to the seventh technical
features, wherein a degree of variation in surface hardness of the
formed corrosion-resistant film in the in-plane direction is
controlled by controlling the flow speed of the solution relative
to the surface of the base material.
[0020] Ninth technical feature: The manufacturing method of the
magnesium-based medical device according to the seventh or eighth
technical feature, wherein the base material is immersed in a
solution which contains phosphorous ions and calcium ions thus
forming the corrosion-resistant film containing calcium phosphate
on the surface of the base material.
[0021] The inventors of the present invention have found that
although it is difficult to control a corrosion resistance period
with respect to the corrosion resistance in a living body only when
the corrosion-resistant film is simply formed, the smaller the
variation in hardness of the film the more the corrosion resistance
period can be prolonged, and have arrived at the present invention
based on such finding.
ADVANTAGE OF THE INVENTION
[0022] According to the magnesium-based medical device of the
present invention, a degree of corrosion resistance can be adjusted
in a wide range of period so that the device can maintain a
sufficient strength for a desired period and disappears after a
desired period.
[0023] Further, by forming the corrosion-resistant film which
contains calcium phosphate, when the magnesium-based medical device
is embedded in a periphery of the bone tissue, the formation of a
bone is accelerated by the calcium phosphate film thus enhancing
the bonding property of a material and the bone. The surface on
which calcium phosphate is deposited exhibits high soft tissue
compatibility and hence, the device exhibits high soft tissue
compatibility when embedded in a blood vessel.
[0024] Further, it is possible to use the magnesium-based medical
device as a regenerative medical device which replaces a bone which
is regenerated along the decomposition and absorption of a
magnesium material such as an artificial bone or a bone plate
embedded in a defective part of the bone.
[0025] According to the manufacturing method of the magnesium-based
medical device of the present invention, it is possible to adjust
the corrosion resistance of the film in conformity with a corrosion
resistance period and a disappearance period which are determined
based on a material of the base, a kind, a size and a purpose of
use of the device used, the individual specificity of a living body
and the like.
[0026] Further, since a voltage or an electric current is not
applied to the base material in forming the corrosion-resistant
film, it is possible to form a desired film over the whole surface
of the base irrelevant to a shape of the device. Further, since the
relative speed between the base material and the solution is
controlled, it is possible to change the homogeneity of the film in
a versatile manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 A photograph showing a surface of untreated pure
magnesium which is polished.
[0028] FIG. 2 A five-time enlarged photograph of the surface of the
pure magnesium shown in FIG. 1.
[0029] FIG. 3 A photograph showing a surface of pure magnesium
treated at a rotational speed of 0 rpm in an example 1.
[0030] FIG. 4 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 3.
[0031] FIG. 5 A photograph showing a surface of pure magnesium
treated at a rotational speed of 30 rpm in the example 1.
[0032] FIG. 6 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 5.
[0033] FIG. 7 A photograph showing a surface of pure magnesium
treated at a rotational speed of 60 rpm in the example 1.
[0034] FIG. 8 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 7.
[0035] FIG. 9 A photograph showing a surface of pure magnesium
treated at a rotational speed of 120 rpm in the example 1.
[0036] FIG. 10 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 9.
[0037] FIG. 11 A photograph showing a surface of pure magnesium
treated at a rotational speed of 1440 rpm in the example 1.
[0038] FIG. 12 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 11.
[0039] FIG. 13 A photograph showing a surface of pure magnesium
treated at a rotational speed of 2880 rpm in the example 1.
[0040] FIG. 14 A five-time enlarged photograph of the surface of
pure magnesium shown in FIG. 13.
[0041] FIG. 15 A graph which exemplifies a degradation speed in a
culture medium of pure magnesium whose surface is treated with the
rotation at different rotational speeds.
[0042] FIG. 16 A graph showing a cumulative quantity of magnesium
dissolved in a culture medium from pure magnesium which is
subjected to surface treatment with the rotation at different
rotation speeds.
[0043] FIG. 17 A graph showing surface hardness of a film formed on
a surface of a pure magnesium which is subject to surface treatment
with the rotation in a calcium phosphate solution.
[0044] FIG. 18 A longitudinal cross-sectional elevation view
showing a state in which the base material is rotated while being
immersed in the solution.
[0045] FIG. 19 A plan view of a treated surface indicating
measuring points of a Vickers hardness test in an example 1.
[0046] FIG. 20 A plan view of a treated surface indicating
measuring points of a Vickers hardness test in an example 4.
[0047] FIG. 21 A graph showing a change of a corroded area ratio
(pure magnesium extruded material).
[0048] FIG. 22 A graph showing a change of a corroded area ratio
(AZ31 extruded material).
[0049] FIG. 23 A graph showing a change of a corroded area ratio
(0.3% Al--Mg extruded material).
[0050] FIG. 24 A photograph showing a surface of a screw in an
example 6 to which only polishing is applied.
[0051] FIG. 25 A photograph showing a surface of a screw having a
film which is treated at a rotation speed of 0 rpm in the example
6.
[0052] FIG. 26 A photograph showing a surface of a screw having a
film treated at a rotation speed of 1440 rpm in the example 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0053] The present invention which has the above-mentioned
technical features is explained in conjunction with embodiments
hereinafter.
[0054] A base material of a medical device according to the present
invention is directed to, in addition to pure magnesium, magnesium
alloys which contain Mg as a main component and further contain a
second component. The base material, in general, contains the
second component with a quantity not more than 1/3 of the limit
concentration of the second component element for its solid
solution in magnesium. Also in such a case, it is needless to say
that the inclusion of inevitable impurities is allowable. For
example, the base material is allowed to contain impurities of not
more than 0.05 atomic %.
[0055] The base material preferably contains a quantity of second
component such that the solid solution limit concentration of the
second component as an element is not more than 1/4 with respect to
magnesium. As a specific example of the element which constitutes
the second component, it may be possible to name Au, Ir, Mn, Zr,
Bi, Co, Zn, Ga, Ag, Al, Li, Ce, Pr, La, Th, Nd, Ca, Yb, Rb, Y, Gd,
Dy, Tm, Er, Lu, Sc, In or the like excluding elements which form
substantially no solid solutions with magnesium or elements which
evidently have damaging property to a living body.
[0056] Further, a grain size of the magnesium alloy is not more
than 1/4 of a minimum portion of the magnesium alloy. The alloy can
acquire desired dynamic characteristics such as strength, work
hardening property, ductility by controlling a kind, quantity and a
grain size of the second component.
[0057] With respect to the configuration of the base material such
as a shape and a size of the base material, the base can take any
arbitrary configuration corresponding to an object of an
application.
[0058] According to the present invention, as a method of
controlling corrosion of the base material made of magnesium or the
magnesium alloy, by generating a flow of a treatment solution on a
surface of the base plate, it is possible to form a film in such a
manner that variation in hardness of the base material, that is,
variation in the constitution or the structure of the film can be
adjusted.
[0059] The film formed on the surface of the base material by the
method of the present invention functions as a corrosion-resistant
film of the base material, and can suppress the degradation and the
dissolution of the base material in an environment. Further, when
the method of the present invention is applied to a medical
biodegradable magnesium material, a period from a point of time
immediately after embedding of the base material in a living body
to a point of time that the degradation of the base material starts
can be prolonged and hence, the base material can surely maintain
an original strength during that period.
[0060] As a method for controlling a flow speed of the solution on
the surface of the base material, for example, a method which
rotates the base material in a solution, a method which oscillates
the base material vertically or laterally in a solution, or a
method which stirs a solution or the like is named. A flow speed of
a solution on the surface of the base material depends on a
relative speed between the surface of the base material and the
solution, and does not depend on a method which moves the base
material. Accordingly, an arbitrary method can be used depending on
a size or a shape of the device.
[0061] The flow speed and the treatment time of the solution can be
suitably changed corresponding to the composition of the base
material, and corrosion resistance, biocompatibility or the like of
the desired film. The larger the flow speed, the more the
homogeneity of the film to be formed is improved. Usually, the
longer the treatment time, the larger a thickness of the film
becomes.
[0062] The method of the present invention is applicable irrelevant
to the composition or the structure of the base material and hence,
the base material can maintain a desired strength-ductility balance
and the like without incurring the rapture of the composition or
the structure thereof.
[0063] According to the method of the present invention, the
surface film is formed along with the deposition of a solute and
hence, the structure, the thickness, the composition and the like
of the film can be changed in a versatile manner whereby corrosion
resistance and the biocompatibility of the film can be
adjusted.
[0064] The composition, the configuration and the like of the film
can be controlled in a versatile manner corresponding to conditions
such as a flow speed of a solution, a treatment time, a kind and
concentration of a using treatment solution, for example.
[0065] With respect to a treatment solution or an environment, it
is desirable that the solution contains an element which
contributes to the improvement of corrosion resistance of magnesium
material. As a specific example of a component of the treatment
solution used in the present invention, a salt of a phosphoric
acid, a silicic acid or an aluminic acid, and a salt or a complex
of calcium or the like can be named. To be more specific, for
example, sodium biphosphate, dibasic sodium phosphate, sodium
silicate, sodium aluminate, aluminum hydroxide, calcium chloride, a
calcium complex and the like can be named. These elements can be
used in a single form or two or more kinds of elements may be used
in combination.
[0066] Besides a case where a content is deposited due to bonding
of ions in a solution such as calcium phosphate, for example, when
a solution which contains Al ions is used, Al can be taken into a
film as oxide of Al or a composite oxide of Al and Mg. In this
manner, by changing the condition such as composition or
concentration of a treatment solution, for example, it is possible
to allow a film to take an element in a solution thereinto.
[0067] According to the method of the present invention, with the
use of the solution which contains phosphate ions and calcium ions,
calcium phosphate is deposited on the surface of the base material
and is taken into the base material. It is possible to adjust a
quantity of calcium phosphate taken into the film based on
concentration of phosphate ions and concentration of calcium ions
in the solution, a treatment time and a flow speed of the
solution.
[0068] As such a treatment solution, for example, it is possible to
use a calcium phosphate solution which is prepared by removing
chloride ions which promote dissolution of magnesium while using a
pseudo body fluid. To be more specific, a Hank's balanced salt
solution or a culture medium which is prepared using phosphate and
calcium can be exemplified as the treatment solution, and these
Hank's balanced salt solution and the culture medium are useful as
solutions which can easily deposit calcium phosphate.
[0069] Calcium phosphate which is deposited on the surface of the
base material changes, due to taking magnesium into the structure
thereof, the composition and the structure of the film based on a
flow speed of a solution and a treatment time. Further, as the
homogeneity of the film becomes higher and the structure of the
film becomes denser, the corrosion resistance of the base material
becomes higher and hence, it is possible to adjust a
degradation-suppressed time of the base material at an initial
stage of embedding the device into a living body within a wide
range of period.
[0070] Further, the composition and the structure of calcium
phosphate in the film directly influence biocompatibility in a
living body and hence, biocompatibility can be controlled by
controlling a treatment time.
[0071] Calcium phosphate improves bone conduction between a bone
and a material by promoting the formation of the bone, and also
exhibits favorable affinity with a vascular endothelial cell. Due
to such a characteristic, the device which exhibits extremely high
biocompatibility on a treated surface thereof can be realized.
Accordingly, when the medical biodegradable device which is treated
in such a manner is embedded in a living body, a surface of the
device is suitably bonded to a peripheral tissue and exhibits
favorable affinity with cells of the peripheral tissue and hence,
the surface of the device exhibits high biocompatibility.
Accordingly, for example, there is no formation of thrombus and
hence, it is expected that curing of the peripheral tissue starts
from an initial stage of embedding and curing is finished
early.
[0072] Further, recently, the medical treatment which promotes
curing of an affected part by supplying a medicament to the
affected part from a surface of a living body material is carried
out. In taking calcium phosphate which is liable to absorb protein
or the like into a surface, when the medicament or protein is added
to a treatment solution, it is possible to take these materials
into a film. Accordingly, it is also possible to manufacture a
medical device which holds various kinds of medicaments necessary
for speeding up curing. Further, with the coupled use of a
conventional slow releasing technique in which a medicament is
contained in calcium phosphate, it is also possible to release the
medicament slowly.
[0073] For example, when the device is used for fracture fixation,
considered is a medical treatment in which protein or the like
which is a bone growth factor is taken into a film, protein or the
like is slowly released from a surface of the film after the device
is embedded in a living body thus promoting the formation of a bone
and eventually promoting curing of fracture.
[0074] Further, when the device is a stent, by allowing the film to
hold a medicament for preventing restenosis which occurs due to
abnormal growth of vascular endothelial cells caused by continuous
mechanical stimulation to a blood vessel wall from the stent, a
medicament is supplied from a surface of the stent thus providing
the medical treatment which prevents the abnormal growth of
vascular endothelial cells.
[0075] Further, a blood vessel wall having an affected part
exhibits a low strength and low resiliency compared to a normal
blood vessel wall and hence, the blood vessel wall having the
affected part cannot recover the strength and resiliency of the
normal blood vessel wall when the stent merely expands the blood
vessel wall by pushing. However, according to the present
invention, it is also possible to provide the medical treatment
which slowly releases a medicament for promoting the repair of the
blood vessel wall from a surface of the stent.
[0076] Further, for example, by embedding a device which carries a
medicament thereon (a medicament slow releasing medical device) in
a bone of a patient suffering from osteoporosis, it is possible to
provide the medical treatment which promotes the increase of bone
quantity by slowly releasing the medicament from the device.
[0077] Hereinafter, the present invention is explained in further
detail in conjunction with examples. However, the present invention
is not limited to these examples in any ways.
EXAMPLES
Example 1
[0078] As a base material, pure magnesium (purity: 99.9%, grain
size: 1 .mu.m) whose surface is polished is used.
[0079] As shown in FIG. 18, a base material (A) is mounted on a
rotation device. The base material (A) is immersed in a phosphoric
acid buffer solution which contains calcium ion (5) at a
temperature of 37.degree. C. while rotating the base material (A)
at rotation speeds of 0 rpm, 30 rpm, 60 rpm, 120 rpm, 1440 rpm and
2880 rpm. Thereafter, the base material (A) is immersed for 10
minutes thus forming a film containing calcium phosphate on a
surface of the base material (A).
[0080] In the rotation device shown in FIG. 18, a specimen rotating
jig (2) which fixes the base material (A) thereto by an adhesive
agent is fixed to a lower end of a main shaft of a motor (3).
[0081] A quantity of the solution (5) sufficient to immerse the
specimen rotating jig (2) in the solution (5) is stored in a
container (4). The container (4) is housed in the inside of a
temperature controlled water bath (6) so as to hold the solution
(5) at a predetermined temperature (7) in the temperature
controlled bath (6). A support strut (8) is provided for holding
the motor (3) at a height which allows the rotation of the base
material (A) in the solution (5).
[0082] Here, a surface of the base material described hereinafter
means a lower surface of the base material (A) in FIG. 18. The
rotation speeds of the base material (A) of 0 rpm, 30 rpm, 60 rpm,
120 rpm, 1440 rpm, and 2880 rpm correspond to linear flow speeds of
0 m/s, 0.02 m/s, 0.04 m/s, 0.08 m/s, 1 m/s and 2 m/s
respectively.
[0083] In this embodiment, as a method of controlling a flow speed
of the solution on the surface of the base material, a method which
rotates the base is adopted.
[0084] FIG. 1 to FIG. 14 show photographs of the appearance of
surfaces treated at respective rotation speeds. The surface (FIG.
3, FIG. 4) treated at the rotation speed of 0 rpm (not rotated)
exhibits the appearance in which white spots are scattered in a
gray background as a whole and hence, it is expected that calcium
phosphate is not homogeneously deposited.
[0085] The surface (FIG. 5, FIG. 6) treated at the rotational speed
of 30 rpm exhibits a non-homogeneous and uneven appearance, wherein
a large number of indentations of several microns are formed.
[0086] The surface (FIG. 7, FIG. 8) treated at the rotation speed
of 60 rpm exhibits the appearance substantially equal to the
appearance when the surface is treated at the rotation speed of 30
rpm. However, the number of depressions of several microns is
smaller than the number of depressions when the surface is treated
at the rotation speed of 30 rpm.
[0087] On the other hand, the surface (FIG. 9, FIG. 10) treated at
the rotation speed of 120 rpm exhibits the appearance in which the
whole surface is covered with a white film, and white spots are
locally observed on the surface in the low-magnification
observation. In the high-magnification observation (FIG. 10), gray
and white spots are locally observed on the white surface. To
compare the surface treated at the rotation speed of 120 rpm and
the surface treated at the rotation speed of 0 rpm, it is
considered that calcium phosphate is deposited more homogeneously
on the surface treated at the rotation speed of 120 rpm.
[0088] The surface (FIG. 11, FIG. 12) treated at the rotation speed
of 1440 rpm exhibits the appearance in which the whole surface is
covered with a white film substantially homogeneously, and
non-homogeneous portion is not observed even in the
high-magnification observation (FIG. 12). It is considered that
calcium phosphate is homogeneously deposited when the surface is
treated at the rotation speed of 1440 rpm.
[0089] From these results, it is evident that the larger the
rotation speed of the base, that is, the larger the flow speed of
the treatment solution, calcium phosphate is deposited uniformly
and homogeneously.
[0090] Further, due to the difference in the appearance of the
formed film, the composition and the structure of calcium phosphate
are changed corresponding to the flow speed of the treatment
solution. When the surface (FIG. 13, FIG. 14) is treated at the
rotation speed of 2880 rpm, in the observation of the whole surface
of the base material, black portions are observed at an edge of a
disk. On the other hand, in the high-magnification observation, the
homogeneous surface film which is free from indentations and
non-homogeneous portions is formed.
[0091] To determine these surface conditions in a more scientific
manner, Vickers hardness of the surface is measured at three points
shown in FIG. 19 where a measurement distance between the points is
set to 4 mm, and an average value of the measured values is set as
surface hardness of the base material. A result of the measurement
is shown in table 1 and FIG. 17. A Vickers hardness test (JIS Z
2244) is performed using a micro-Vickers hardness meter (made by
AKASHI: MVK-E), and the surface hardness is measured by setting a
load of an indenter to 10 gf and a holding time to 15 seconds.
[0092] As shown in following Table 1, compared to the surface
hardness of the untreated surface, the surface hardness of the
surface treated in the solution exhibits a large value irrespective
of the rotation speed. Further, due to the rotation of the base, an
error bar indicative of a standard deviation value of the hardness
shown in FIG. 17 is lowered so that variation in surface hardness
is decreased.
[0093] Since the variation in surface hardness is small, it is
evident that the film formed by rotating the base is homogeneous in
the in-plane direction. The increase of surface hardness implies
that the film structure is more densified. Further, from results of
examples described later, it is found that when the device is pure
magnesium, the larger the surface hardness and the smaller the
variation in surface hardness, the larger a dissolution quantity
can be suppressed. In general, the diffusion of the magnesium ions
toward a solution side from a background is suppressed due to the
densification of the film and hence, it is considered that the
dissolution of magnesium is suppressed when the denseness of the
film is enhanced.
Example 2
Immersion Test
[0094] The base material which is obtained by the example 1 and
deposits calcium phosphate on the surface thereof is immersed in
27.5 ml of culture medium (E-MEM+10% FBS) in the inside of an 5%
CO.sub.2 incubator held at a temperature of 37.degree. C. for 5
days, and the determination of magnesium ions dissolved in the
culture medium is performed by a xylidyl blue method.
[0095] Here, the culture medium is exchanged by 15 ml for every
day, and the quantification is performed using a sampled solution.
A dissolution quantity of magnesium ions is shown in FIG. 15.
Further, a cumulative dissolution quantity of magnesium at each
immersion days is shown in FIG. 16. The base material (FIG. 1, FIG.
2) to which only polishing is applied without applying the
treatment is prepared as a comparison material, and a dissolution
test in the cell-culture solution is also carried out with respect
to this base. The above is summarized in Table 1.
TABLE-US-00001 TABLE 1 Rotation speed Dissolution of specimen
Vickers quantity Dissolution quantity during treatment hardness of
Mg in 1st day/ of Mg (rpm) (Hv) mg/mm.sup.2 L in 5th
day/mg/mm.sup.2 L untreated 36.6 .+-. 4.6 0.279 .+-. 0.014 0.142
.+-. 0.007 0 55.8 .+-. 7.7 0.258 .+-. 0.082 0.075 .+-. 0.045 30
47.4 .+-. 1.2 -- -- 60 54.6 .+-. 2.9 -- -- 120 64.6 .+-. 2.7 0.128
.+-. 0.054 0.041 .+-. 0.019 1440 66.0 .+-. 4.5 0.102 .+-. 0.027
0.083 .+-. 0.042 2880 57.4 .+-. 7.7 -- -- Respective values in
Table indicate an average value .+-. a standard deviation
value.
[0096] The base material to which the treatment is applied with the
rotation exhibits small magnesium dissolution quantity in an
initial stage of immersion into culture medium compared to the base
material (FIGS. 3, 4) to which the treatment is applied without
rotation. It is found that the film formed in a state that the base
material is rotated, that is, the film formed under a control of a
flow speed of the solution exhibits a large effect in the
suppression of dissolution of magnesium. Further, the magnesium
dissolution quantity of the base material to which the treatment is
applied without rotation in an initial stage of immersion is
substantially equal to the magnesium dissolution quantity of the
base to which the treatment is not applied.
[0097] This result shows that the homogeneous film which is formed
by controlling the flow of the solution has an effect of
suppressing the degradation of magnesium material in an initial
stage of immersion. The dissolution quantity of magnesium into the
culture medium is decreased along with the increase of immersion
days irrespective of the treatment condition of the surface of the
base material.
[0098] The dissolution quantity of magnesium from the base material
to which the treatment is applied with the rotation of the base
material is smaller than the dissolution quantity of magnesium from
the base material to which the treatment is applied without
rotation of the base material until the third immersion day.
However, on the fourth immersion day and thereafter, the
substantially same magnesium dissolution quantity is detected
irrespective of presence or non-presence of rotation of the base
material during the treatment. It is found that the influence on
the degradation suppressing effect due to the film exerted by the
different flow speeds of the solution is conspicuous in an initial
stage of immersion.
[0099] On the other hand, to compare the base material to which the
treatment is applied without rotation and the untreated base
material, it is found that the longer the immersion time, the more
the degradation of the base material to which the treatment is
applied without rotation is suppressed. Irrespective of the
presence or the non-presence of the rotation of the base material
during the surface treatment, a total dissolution quantity of
magnesium from a surface of the magnesium material treated with the
calcium phosphate solution is small.
Example 3
Surface Composition of Magnesium-Based Material which is Treated
Under Controlled Solution Flow
[0100] Out of pure magnesium materials which are prepared by the
method explained in the example 1 and which deposit calcium
phosphate on surfaces thereof, the surface compositions of
specimens when the rotation speed during the surface treatment is
set to 0 rpm, 30 rpm, 1440 rpm and 2880 rpm are measured by an
energy-dispersion type X-ray analysis (EDS). The compositions of
the surfaces formed at the respective rotation speeds are shown in
Table 2.
TABLE-US-00002 TABLE 2 Composition of film obtained in mixture
solution of phosphoric acid and calcium Rotation speed
Concentration during treatment (at %) (rpm) O Mg P Ca 0 14.9 84.9
0.2 0.0 30 14.4 84.5 0.7 0.4 1440 20.8 77.7 0.8 0.7 2880 18.1 79.2
1.5 1.2
[0101] The specimens to which the treatment is applied with the
rotation exhibit the high P concentration and the high Ca
concentration compared to the specimen to which the treatment is
applied without rotation. Further, along with the increase of the
rotation speed, P concentration and Ca concentration are increased.
Accordingly, it is found that when a flow speed of the solution on
the surface of the base material is increased, a deposition
quantity of calcium phosphate is increased. It is also found that O
concentration is increased along with the increase of the rotation
speed of the specimen. This suggests a possibility of the increase
of a thickness of the formed film when the flow speed of the
solution on the surface of the base material is increased. From
these results, it is evident that an intake quantity of the film
forming element from the solution can be controlled by controlling
the flow speed of the treatment solution on the surface of the base
material made of the magnesium-based material.
Example 4
Dispersion of Surface Hardness of Magnesium-Based Material Treated
Under Solution Flow Control
[0102] Out of the pure magnesium materials which are prepared by
the method explained in the example 1 and which deposit calcium
phosphate on surfaces thereof, Vickers hardness is measured with
respect to surfaces of specimens by setting the rotation speed at 0
rpm, 30 rpm, 120 rpm, 1440 rpm and 2880 rpm during the surface
treatment at 17 points at measurement intervals of 1 mm as shown in
FIG. 20. In a comparison example, the similar measurement is also
performed with respect to a surface of an untreated material to
which only polishing is applied. In a Vickers hardness test (JIS Z
2244), the measurement is made using a micro-Vickers hardness meter
(made by AKASHI: MVK-E) while setting a load of an indenter to 10
gf and a holding time to 15 seconds. Table 3 shows an
average.+-.standard deviation and the dispersion of measured
values. It is found from this test that the smaller the dispersion
value, the smaller the variation in hardness of the surface of the
specimen in the in-plane direction becomes. That is, this test
shows that the formed film is homogeneous in the in-plane
direction.
TABLE-US-00003 TABLE 3 Relationship among rotation speed, hardness
of film and variation (dispersion) in hardness Rotation speed of
specimen during treatment (rpm) untreated 0 30 120 1440 2880
Vickers hardness (Hv) 43.7 .+-. 2.7 47.6 .+-. 4.8 47.1 .+-. 3.0
47.0 .+-. 1.2 46.5 .+-. 1.8 46.2 .+-. 3.1 Dispersion 7.0 21.7 8.7
1.5 2.9 9.1 *Each numerical value of Vickers hardness in Table
indicates an average value .+-. standard deviation.
[0103] By carrying out the significant difference test of F
distribution based on the dispersion 21.7 in hardness of the
surface to which the treatment is applied at the rotational speed
of 0 rpm, the significance of difference between the dispersion in
hardness of the surface to which the treatment is applied with
rotation and the dispersion in hardness of the surface to which the
treatment is applied without rotation are determined with certain
reliability. In carrying out the significant level 1% one-sided
test, when the dispersion in hardness of the surface to which the
treatment is applied with rotation is smaller than 6.4, it is safe
to say that the dispersion in hardness of the surface to which the
treatment is applied with rotation is significantly smaller than
the dispersion in hardness of the surface to which the treatment is
applied at the rotation speed of 0 rpm with reliability of 99%. In
carrying out the significant level 5% both-sided test, when the
dispersion in hardness of the surface to which the treatment is
applied with rotation is smaller than 7.9, it is safe to say that
the dispersion in hardness of the surface to which the treatment is
applied with rotation is significantly smaller than the dispersion
in hardness of the surface to which the treatment is applied at the
rotation speed of 0 rpm with reliability of 97.5%. In the same
manner, in carrying out the significant level 5% one-sided test,
when the dispersion in hardness of the surface to which the
treatment is applied with rotation is smaller than 9.3, it is safe
to say that the dispersion in hardness of the surface to which the
treatment is applied with rotation is significantly smaller than
the dispersion in hardness of the surface to which the treatment is
applied at the rotation speed of 0 rpm with reliability of 95%.
[0104] In this test, all dispersions in hardness of the surfaces to
which the treatment is applied with rotation of the specimen are
smaller than 9.3 and hence, the dispersion in hardness of the
surface to which the treatment is applied with rotation is
significantly smaller than the dispersion in hardness of the
surface to which the treatment is applied at the rotation speed of
0 rpm with reliability of 95%. This implies that when the surface
treatment is performed with the rotation of the specimen, the
variation in the hardness of the formed film in the in-plane
direction is decreased. Accordingly, it is evident that the formed
film becomes homogeneous by performing the surface treatment while
generating the controlled flow of the solution on the surface of
the base material.
[0105] The dispersion in hardness of the surface to which the
treatment is applied while rotating the specimen at 120 rpm or more
is significantly smaller than the dispersion in hardness of the
untreated surface to which only polishing is applied with
reliability of 95%. This implies that it is possible to form a film
which is more homogeneous than an air-formed film of the base
material by controlling a flow speed of a treatment solution on a
surface of the base material of the magnesium material.
Example 5
Evaluation on Corrosion Based on Atmospheric Corrosion Test of
Treated Film
[0106] Using a pure magnesium extruded material (purity: 99.9%), an
AZ31 extruded material and a magnesium alloy extruded material
containing 0.3 wt % of Al (0.3% Al--Mg extruded material), a film
containing calcium phosphate on a surface thereof is formed by the
method explained in the example 1. Here, a specimen rotation speed
is set to 0 rpm and 1440 rpm.
[0107] 1 g/m.sup.2 of NaCl is placed on a surface of a specimen.
The specimen on which NaCl is placed is held in a temperature
controlled bath in which relative humidity is held at 95% or more
at a room temperature (25.degree. C.). After 1 hour, 2 hours and 4
hours, an image of a total surface of each specimen is photographed
by a CCD camera mounted on a stereoscopic microscope. A total area
of a corroded portion is obtained from the image, and a corroded
area ratio which is a ratio of a corroded area with respect to a
total surface area is obtained. Changes with time of corroded area
ratios of the pure magnesium extruded material, the AZ31 extruded
material and the 0.3% Al--Mg extruded material are respectively
shown in Table 4 and FIG. 21 to FIG. 23.
TABLE-US-00004 TABLE 4 Change with time of corroded area ratio of
film Rotation speed of specimen Corroded area ratio (%) Kind of
base during treatment After After After material (rpm) 1 hour 2
hours 4 hours Pure magnesium untreated 3.6 13.1 22.1 extruded
material 0 2.5 3.8 5.5 1440 0.3 1.7 8.2 AZ31 untreated 4.1 6.6 9.8
extruded material 0 0.9 1.3 2.9 1440 1.3 1.9 2.9 0.3% Al--Mg
untreated 3.3 9.8 17.1 extruded material 0 0.8 1.5 3.6 1440 0.5 0.8
1.4
[0108] Tendency that the corroded area ratio of the specimen
treated at 1440 rpm is lower than the corroded area ratio of the
specimen treated at 0 rpm is found with respect to all
magnesium-based materials. From this result, it is evident that the
corrosion resistance of the magnesium-based material against
chloride ions is enhanced by forming the film under a flow with
controlled speed of a solution on a surface of the specimen.
[0109] Magnesium-based materials are used not only as a biomaterial
but also as a material of a part of a transport apparatus such as
an automobile or a material of a casing of a house hold electric
appliance or a communication apparatus. The corrosion of these
materials is mainly caused by chloride ions. Since the corrosion
due to NaCl placed on the surface can be suppressed by the surface
treatment according to the method of the present invention, it is
evident that the surface treatment method of the present invention
is applicable to magnesium-based materials used in various
applications.
[0110] Further, from Table 4 and FIG. 21 to FIG. 23, it is found
that in all magnesium-based materials, irrespective of the presence
or the non-presence of rotation during the surface treatment, the
corroded area ratio of the specimen treated with the calcium
phosphate solution is lower than the corroded area ratio of the
untreated specimen. From such a result, it is evident that the
surface film containing calcium phosphate exhibits corrosion
resistance against chloride ions.
Example 6
Evaluation on Corrosion Resistance by Cyclic Dry and Wet Test of
Treated Film of Screw-Shaped Specimen
[0111] A surface of a screw (AZ31, nominal size: M3.times.20 mm)
made of a magnesium alloy is polished with a metal-use polishing
agent, and a film containing calcium phosphate is formed on the
surface of the screw in the same manner as the example 1. Here, a
rotational axis of the screw specimen is set as a center axis of
the screw in the longitudinal direction, and the screw is fixed to
a jig with a screw head directed downwardly and a distal end of the
screw directed upwardly. A rotation speed is set to 0 rpm and 1440
rpm.
[0112] 1 g/cm.sup.2 of NaCl is placed on a surface of the untreated
specimen to which only polishing is applied and a surface of the
specimen treated at 0 rpm or 1440 rpm, and these specimens are held
in a temperature controlled box in which relative humidity is held
at 95% or more. Then, a cyclic dry and wet test in which 1 cycle is
constituted of 24 hours in total where temperature is switched to
25.degree. C., 50.degree. C. and 25.degree. C. for every 8 hour is
carried out 2 cycles repeatedly. After every 24 hours (completion
of every 1 cycle), the screw specimen is lightly cleaned with
ultra-pure water, and NaCl is placed on the screw specimen again.
After 1 hour, 2 hours, 4 hours, 24 hours and 48 hours from starting
of the test, a surface of each specimen is photographed by a CCD
camera mounted on a stereoscopic microscope.
[0113] FIG. 24 to FIG. 26 respectively show stereoscopic microscope
images of surfaces of the respective screw specimens after 48 hours
from starting of the test (after completion of 2 cycles). In all
screw specimens, corrosion occurs along valleys of threaded
grooves. Then, the number of threaded grooves in which the
corrosion occurs is counted with respect to twenty threaded grooves
formed on a portion of the screw specimen arranged in the direction
toward a distal end of the screw specimen from the head of the
screw specimen, and the number is summarized in Table 5.
TABLE-US-00005 TABLE 5 Frequency of occurrence of corrosion in
cyclic dry and wet test of screw-shaped base Rotation speed Number
of threaded grooves in which corrosion of specimen occurs per
twenty threaded grooves (pieces) during treatment After After After
After After (rpm) 1 hour 2 hours 4 hours 24 hours 48 hours
untreated 8 9 13 16 19 0 6 7 9 16 17 1440 4 5 10 13 14
[0114] In all times after starting the test, the number of threaded
grooves in which the corrosion occurs in the screw specimen treated
at 1440 rpm is smaller than the number of threaded grooves in which
the corrosion occurs in the screw specimen treated at 0 rpm. From
such a result, it is evident that the enhancement of the corrosion
resistance of the magnesium-based material due to the film
formation under a flow speed control of a treatment solution on a
surface of the base material is effective irrespective of a shape
of the base material.
[0115] With respect to the screw specimens after 48 hours from
starting of the test (after completion of 2 cycles), to observe a
corrosion state of a background magnesium material, a corroded
product is removed using a chromic acid solution. With respect to
twenty threaded grooves from which the number of threaded grooves
on which the corrosion occurs is counted, an arbitrary portion
having a length of 300 .mu.m along the valley is measured by a
laser microscope, and a maximum height (Ry: a total of a crest
height and a valley height of concaves and convexes included in a
standard length) which is a kind of line coarseness is obtained. In
this test, it is considered that the larger the Ry, the deeper a
corroded hole becomes.
[0116] Among Ry obtained with respect to twenty threaded grooves,
measured values from the top to the fifth are shown in Table 6.
TABLE-US-00006 TABLE 6 Result of atmospheric corrosion test of
screw-shaped base after 48 hours Rotation speed of specimen during
treatment Top five measured values of Ry (rpm) (.mu.m) of corroded
portions Only polishing 70.1 47.2 45.6 44.1 37.3 0 44.5 32.3 29.4
28.5 28.3 1440 44.5 28.1 26.2 22.9 20.9 Ry: maximum height of
corroded portion which occurs in valley portions of threaded
grooves.
[0117] Here observed is tendency that a depth of the corroded hole
in the screw specimen treated at 1440 rpm is smaller than a depth
of the corroded hole in the screw specimen treated at 0 rpm. From
this result, it is evident that the formation of a film under a
control of a flow speed of a solution has an effect of suppressing
a progress of the corrosion of the magnesium material in the depth
direction.
[0118] Further, irrespective of the presence or the non-presence of
the rotation during the surface treatment, a depth of the corroded
hole in the screw specimen treated with calcium phosphate solution
is smaller than a depth of the corroded hole in the screw specimen
to which only polishing is applied. From this result, it is evident
that a film containing calcium phosphate is effective in the
enhancement of the corrosion resistance of the magnesium material
irrespective of a shape of a base material.
Example 7
Evaluation on Corrosion Resistance of Magnesium-Based Material
Treated with Addition of Ultrasonic Oscillations by Immersion
Test
[0119] A pure magnesium extruded material (purity: 99.9%) and an
AZ91 cast material are used. The specimen is fixed to a distal end
of an ultrasonic oscillation generator using an instantaneous
adhesive agent. While applying ultrasonic oscillations of frequency
of 30 kHz and amplitude of 100 .mu.m to the specimen, the specimen
is immersed in a calcium phosphate solution which is the same as
the solution used in the example 1 for 10 minutes thus forming a
film containing calcium phosphate in a surface thereof. As a
comparison material 1, in the method explained in the example 1, a
film is formed on a surface of a pure magnesium extruded material
and a surface of an AZ91 cast material while rotating the specimen
at a rotation speed of 1440 rpm.
[0120] With respect to the specimens on which the surface film is
formed by the above-mentioned respective methods, a portion of the
surface of the specimen except for a predetermined area of the
surface where the film is formed is covered with a silicone resin,
and the specimen is immersed in a 3.5 wt % NaCl-0.05M boric acid
aqueous solution (pH: 9.3, NaCl boric acid buffering solution)
aerated at room temperature for 1 hour. Thereafter, determination
of magnesium ions dissolved in the NaCl boric acid buffering
solution is performed by a xylidyl blue method, and a dissolved
quantity of magnesium ions per unit area of the surface of the
specimen is obtained. The dissolved quantity of magnesium ions is
shown in Table 7.
TABLE-US-00007 TABLE 7 Change of dissolved quantity of magnesium
ions due to difference in flow generating means Kind of base Method
of generating flow Dissolved quantity material on surface of base
material per unit area (mg/cm.sup.2) pure Ultrasonic oscillations
0.14 .+-. 0.07 magnesium Rotation (1440 rpm) 0.19 .+-. 0.06 AZ31
Ultrasonic oscillations 0.67 .+-. 0.02 extruded material Rotation
(1440 rpm) 0.71 .+-. 0.03 Each numerical value in Table indicates
an average value .+-. standard deviation.
[0121] In both of the pure magnesium extruded material and the AZ91
cast material, the dissolved quantity of magnesium from the
specimen having the film formed by applying ultrasonic oscillations
is substantially equal to the dissolved quantity of magnesium from
the specimen having the film formed with rotation at 1440 rpm.
Accordingly, it is found from this example that, in addition to the
means which applies the rotation to the base material, the means
which applies ultrasonic oscillations to the base material is also
effective as a means for generating a controlled flow between the
surface treatment solution and the surface of the base
material.
* * * * *